1. Field of the Invention
The present invention relates to a communication system transmitting and receiving moving picture data or the like on the basis of the MPEG-2 standard or the like, and a control method thereof.
2. Description of the Related Art
It is well known that there are data processing systems reproducing a moving picture data recorded in a recording medium and carrying out dubbing by using an isochronous transfer on the basis of the IEEE Std 1394-1995 or the like. Next, one example of these data processing systems is described.
FIG. 4 is a block diagram of a data processing system 400. In this example, a system using a disk as a recording medium is described.
The data processing system 400 comprises a data processor 410 on a transmission side, a data processor 420 on a reception side, and a communication cable 430 connecting these processors. Further, the data processor 410 on the transmission side is connected with a disk 401 and a display device 402 on the transmission side, and the data processor 420 on the receptions side is connected with a disk 404 and a display device 403 on the reception side.
The moving picture data in the disk 401 on the transmission side is read by a recording and reproducing unit 411 of the data processor 410 on the transmission side, and transmitted to a display control unit 412. In the display control unit 412, decode processing is performed to display the moving picture on the display processor 402. Further, the moving picture data read by the recording and reproducing unit 411 is inputted into a digital interface unit 413 in accordance with the IEEE Std 1394-1995 or the like. Then, the moving picture data is subjected to a predetermined packetization in the digital interface unit 413, and inputted to a digital interface unit 421 of the data processor 420 on the reception side through the communication cable 430. The digital interface unit 421 is based also on the IEEE Std 1394-1995 or the like. In the data processor 420, the moving picture data transmitted from the data processor 410 is decoded by the display control unit 422, displayed on the display device 403, and recorded in the disk 404 by a recording and reproducing unit 423.
When carrying out dubbing, an encryption processing can be performed on the moving picture data to prevent an unauthorized copying using a copy protection. In this case, in the recording and reproducing unit 411 of the data processor 410 on the transmitting side, the moving picture data read from the disk 401 is encrypted in a various mode according to a limitation level of the copy. Further, in a case of the moving picture data having no copy limitation, the encryption processing is not performed.
In the data processor 410 on the transmission side, the moving picture data having copy limitation is encrypted and outputted, and the key for deciphering the encryption is transmitted only to the device authenticated by the processor 410, in order to prevent altering, tapping or the like. The encrypted moving picture data is inputted into the digital interface unit 413, and into the digital interface unit 421 of the data processor 420 on the reception side through the communication cable 430. In the data processor 420, the inputted moving picture data is subjected to calculation using the above-described key, and the encrypted moving picture data is decrypted. Then, the data processor 420 on the reception side can decode the decrypted moving picture data in the display control unit 422 so as to enable display on the display device 403 or record it in the disk 404 by the recording and reproducing unit 423.
FIG. 5 is a schematic view when the moving picture data in accordance with the MPEG-2 Transport Stream (hereinafter, referred to as the MPEG2-TS) is packetized to an isochronous packet in accordance with the IEEE1394-1995 standard.
A data column 501 of the moving picture data recorded in the disk 401 is read by the recording and reproducing unit 411, and inputted into the digital interface unit 413 by each MPEG2-TS packet 502 of 188 bytes. Time stamp data is added to each MPEG2-TS packet 502 as a header which becomes a source packet 503. Then, the source packet 503 is divided into 8 data blocks 504. Further, several data blocks 505 (in this example, 4 data blocks) are made into one isochronous data 506 according to a bit rate of the MPEG2-TS data. To each isochronous data 506 is added a common isochronous packet (CIP) header 507, an isochronous packet header 508 and a CRC data 509, and the isochronous data becomes an isochronous packet 510. In the present example, a packet consisting of 4 data blocks 505 is transmitted in each isochronous cycle, and the bit rate of the MPEG2-TS is about 6.016 Mbps.
The isochronous communication is described in the IEEE1394-1995 standard. The encrypting technique is described in the “5C Digital Transmission Content Protection White Paper Revision 1.0” and the “Digital Transmission Content Protection Specification Volume 1_Revision 1.2a (Informational Version)”. Further, a method for transmitting the MPEG2-TS data as the isochronous packet on the basis of the IEEE1394 standard is described in the “IEC 61883-4: Consumer audio/video equipment-Digital interface-Part 4: MPEG2-TS data transmission”.
However, in the above data processing system, when the moving picture data is dubbed by transmitting the data using the above-described isochronous transfer from the data processor 410 to the data processor 420, time required for dubbing is the same as its reproducing time. For example, in the case of the moving picture data of one hour, one hour is also required for its dubbing. Further, if the processing capability of the data processor 420 on the reception side is inferior to the data processor 410 on the transmission side with respect to a transfer rate of the moving picture data, the transmitted moving picture data cannot be dubbed.
That is, in the data processing system 400, when the data is transferred from the data processor 410 to the data processor 420, the most suitable data transferring for both sidescan not be performed because consideration is not given to the data processor 420.